Salesforce Error: 400 Bad Request: Invalid Cross-Reference Key

This happens when the field that is throwing the error was expecting a correct ID.

This means that the field was given a Salesforce ID, but the ID is not the correct object type or format. For example of the screenshot, the Record Type ID field was expecting a Salesforce ID of a record type, and not anything else such as an Account, Opportunities, or Leads.

Solution:

Make sure you are mapping the right pill to the right field so that the Object ID matches with the expected type.